Is Shampoo Dangerous?

As a scientist, it is part of my job to keep tabs on new scientific discoveries and recent publications. It was in this context that I recently ran into a fascinating paper by researchers at the University Of Cambridge looking into how formaldehyde (a known carcinogen) selectively destroys BRCA2 – a protein in the cell that is known to suppress the formation of tumors. In fact, BRCA2 is a highly studied gene in medical science since its inactivation by random mutation has been strongly associated with increased risk of certain types of cancer – in particular breast and uterine tumors. It’s a wonderful piece of scientific ingenuity that sheds light on a fascinating new mechanism through which damaging chemicals can damage the cell in very specific ways. On the other hand, as someone interested in science in the media I also keep an eye on how the most read publications in the English-speaking world report on science. One of the most eye-catching titles of the past week was published in The Sun tabloid, and reads Booze, shampoo and car fumes ALL ’cause cancer – and now scientists think they know why’. You can imagine my confusion when I realized that the source for this article were the “Cambridge boffins” who ha published the article on formaldehyde – driven BRCA2 degradation.

The title names three potential causes for cancer: booze, shampoo and car fumes. interestingly, two of these things – namely booze and car fumes – do actually significantly increase the risk to be diagnosed with a tumor – even though formaldehyde is only partially responsible for this effect. Both excessive alcohol consumption and extremely polluted surroundings lead to constant inflammation – which leads to the body constantly having to repair itself. When this happens, cells have to divide much more frequently than intended, which increases the chance of random mutations being inserted into the DNA and therefore the chance of a tumor forming (for more on the relationship between inflammation and cancer, check out my blog series). For example, alcohol consumption drives liver inflammation, which can lead to cirrhosis, increase the risk of hepatitis and eventually cause liver cancer.

However, the third potential cause for cancer – shampoo – has not been shown to cause cancer by any reputable epidemiological studies published in peer-reviewed journals. The rationale behind adding a cosmetic product to the no-go list is that these types of products have recently been accused to contain quaternium-15 and other chemical products that release formaldehyde. In fact, some major brands have caught the attention of major media outlets recently by removing these compounds from their products following pressure on social media. On the surface, this all makes sense. Formaldehyde causes cancer. Shampoo contains formaldehyde-releasing products. Therefore shampoo gives you cancer – aside from those that are labelled formaldehyde-free. Sounds good. Right?

The reason this logical train-of-thought doesn’t actually translate in an increased risk of cancer for those who use shampoo (or more shampoo, such as people with long hair or those who wash their hair every day) lies in quantities. As the old adage says: everything in moderation (the rest of it goes even moderation, which is not really appropriate in the context of formaldehyde exposure). Formaldehyde is everywhere – even our bodies produce some as a by-product of our metabolism. There is no such thing as a formaldehyde-free environment since it is a natural component of living things. What studies refer to when they note that formaldehyde causes cancer is high exposure to it. For example, I work in a laboratory which uses formaldehyde all the time and the rules for using it and disposing of it are very strict to ensure neither scientists nor our surrounding environment is contaminated. Similarly, other people who work with this chemical in high quantities and for extended periods of time have been shown to have an increased risk of contracting certain types of cancer. For instance, those working in the funeral industry (where formaldehyde is used to embalm cadavers) are at increased risk of blood and brain cancer. The quantity of formaldehyde present in any cosmetic product is simply not even on the same scale of what would be necessary to drive tumor formation. The classic example that is used in popular science when talking about formalin is fruit. Say you were to wash your hair with 6ml of shampoo (that’s actually quite a lot, but let’s say you have long, luscious locks). That contains 54 micro-grams of formaldehyde, which is the equivalent of one-thousandth of an average pear (we’re talking about formaldehyde that is naturally occurring in the pear, not about formaldehyde contamination). If this is putting you off pears, bear in mind that the amount of formaldehyde in shampoo is around one-five-hundredth of a beetroot, or around one-two-hundred-and-fiftieth of a plum. Long story short, the produce with the least amount of naturally occurring formaldehyde are cucumbers, which still have about 36 times more formaldehyde than that 6ml of shampoo you use to get yourself clean. The bottom line is that shampoo introduces an insignificant amount of formaldehyde in the body (if you would like some more back-of-the-envelope calculations, read this).

What does this mean in practical terms? The sad thing the media often ignores when covering genuinely exciting science news is the genuine potential for intervention and what these discoveries can do to change patient’s lives. People who already have damaging mutations to BRCA2 and are already at a much higher risk to develop a tumor can really be hurt by the normal, everyday doses of formaldehyde (from food, the air and yes, in very small measures shampoo as well as more clearly toxic things like cigarettes and car fumes). Therefore, the authors of the study suggest that these patients take special medication that “scavenges” formaldehyde throughout the body, reducing the risk of even more BRCA2 molecules being damaged – yet another very significant way in which our understanding of the biology of cancer is changing how we care for patients.